> Paul Crowley (Paul@crowleyp.demon.co.uk) wrote:> : The fact that most such species are arboreal today does not mean> : that their ancestors were. Ancestor species are most likely to > : be general-purpose, non-specialized and widely spread; all this> : implies terrestriality. Whereas, purely arboreal species are > : likely to get isolated in their own patch of forest, as we see> : with the many species of gibbon and the two species of orang.> > Given the anatomical evidence for arboreality in almost all modern and> fossil primates (grasping hands and feet, nails, skeleton adapted to> arboreal locomotion--vertical clinging and leaping using a tail for> balance, above-branch quadrupedalism with a long back and tail for> balance, below-branch suspensory climbing with a short back and no tail),> to claim terrestriality puts the burden of proof on the claimant.

"Proof" is a long way off. Now it's the weight of the evidence
against elementary logic; and I'm saying the fossil evidence has a
taphonic bias. Which is most likely to find itself jumping into
estuarine mud: a chimp or a proboscis monkey? Which is most likely
to find itself in trees over such mud: a gibbon or a gorilla? I can
see a juvenile gibbon, searching for new territory, being driven by
a hostile male to the edge of its territory over an estuary, taking
unwonted risks and falling into such mud. The complete absence of
chimp and gorilla fossils must give us pause to think.

> : Surely it should be the other way around -- foraging the trees and > : eating it on the ground? Intra-species competition is a much more > : potent selection force than predation, and high quality food that > : can be collected quickly is generally in trees, i.e. fruit and nuts. > : If the species goes around in large troops (as many do) then the > : individuals that can grab the most when they find a fruit-laden tree > : (or branch) will be the ones to leave most descendants. > : What do field observations tell us on this?> > Catarrhine monkeys, particularly colobines, are adapted to eating> low-quality, unripe fruit and mature leaves.

Colobines do not have cheek-pouches. They're a long-establised
specialization of the cercopithecinae which are mostly larger ground-
adapted but tree-feeding species such as baboons and macaques. Such
a distinctive and important feature would not have developed for low-
quality food. Anyway, not much food is found on the ground.